During the lifetime of a well, the equipment used to construct and produce from the well may interact with different types of fluids, such as drilling fluids, stimulation fluids, completion fluids, formation fluids, fluids injected into an adjacent well, etc. Depending on their chemical properties, these fluids, which may be characterized generally as “corrosive fluids,” may react with some of the materials within the well and with each other, causing corrosion, scaling and/or other degradation of the equipment within the well. Casing, liner, and cement lining the annulus between casing or liner and the wellbore wall are conventionally employed to enhance the stability of the well during drilling operations and/or production operations.
During the drilling of a wellbore, the drilling fluid contacts materials within the borehole such as drilling equipment, and any construction material such as casing and liner strings which may be in place within the wellbore. The drilling fluid may also interact with the formation and the formation fluid. The drilling fluid may invade into the formation and remain in reservoir and non-reservoir sections of the formation, or may later be removed with formation fluids during production. During a later stimulation stage, the stimulation fluid may be in contact with casing and liner strings, stimulation equipment, any other equipment in the borehole, the formation, and formation fluids. The stimulation fluids may remain in the formation until at least a portion of the stimulation fluid is removed with the formation fluid during production. Fluids may be injected into the well or into an adjacent well and may pass through the formation and be produced at a production well. During the production stage, completion fluid, residual drilling fluid, residual stimulation fluid remaining in the formation, and injected fluids may interact with each other, and with exposed surfaces of the casing, liners, tubing, the formation, and the formation fluid. The formation fluid may interact with exposed surfaces of the casing, liners, tubing, and the formation as it travels to the surface. Although the downhole equipment may be in contact with such fluids for only short periods of time, such as during drilling or stimulation, considerable degradation of equipment may take place due to the contact and interaction with the fluids.
After construction of the well, the formation fluid, produced fluid, residual drilling fluid, and residual stimulation fluid may be in contact with the casing, liner, and other components for longer periods of time. Although production wells may be equipped with corrosion resistant materials, with time, and particularly when aggressive fluids are produced, the integrity of these materials and materials with limited corrosion resistance may be reduced, which may enable the corrosive fluids to contact the casing, liner, tubing or other well construction equipment.
In addition, exposing cement within a well to formation fluids, drilling fluids, completion fluids, injected fluids, stimulation fluids, and mixtures thereof may cause the cement to degrade and crack. As the cement cracks, outer surfaces of the metal casing contacting and supported by the cement may become exposed to produced fluids, formation fluids, drilling fluids, completion fluids, injected fluids, stimulation fluids, and mixtures thereof. The metal and cement may react with such fluids.